I actually see a lot of posts of the sort that you made. I remember my uncle telling me once (he has a small hobby farm in Indiana) that it was his opinion that people overworm their chickens. He sees it as sort of akin to giving a kid some penicillin just because. My uncle's approach is to see if they're exhibiting any symptoms, ex: lethargy etc and after eliminating other possibilities try a worming medication. He always told me that you'll only get resistance if you keep providing it at a regular interval if it's given infrequently it shouldn't be as much an issue. I remember a vet telling me that once too he actually handled farm animals. Anyway everyone has a different way to do things I guess. I try to lean on the side of the conservative because too much of a good thing is still too muchI stopped using Ivermectin as a wormer years ago due to its overuse treating birds for mites causing worm resistance in chickens. It is ineffective as a poultry wormer. It's best to stick with benzimidazoles or levamisole when it comes to worming chickens.
https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1439-0450.1989.tb00635.x
As a matter of fact, mites are showing resistance to Ivermectin in some parts of the country. See the link in post #8:
https://www.backyardchickens.com/th...osage-and-instructions.1351897/#post-22288649
